docs: fix incorrect usage of Promise in page params example (#79804)
The documentation incorrectly used `params: Promise<{ slug: string }>`
in an example and attempted to use `await` in a non-async function.
This commit updates the example to reflect the correct usage:
- `params` should be a synchronous object: `{ slug: string }`
- The page component should be declared `async` if using `await` inside
This fixes a misleading example and aligns it with actual behavior in
the Next.js App Router: [cause]: SyntaxError: await is only valid in
async functions and the top level bodies of modules
Co-authored-by: JJ Kasper <jj@jjsweb.site>
next.js
323ec0ae - docs: fix incorrect usage of Promise in page params example (#79804)
